The invention pertains to a heating device for a corrugated cardboard facility and, more particularly, to such a heating device having several heating plates arranged sequentially in the advancing direction of the sheet of corrugated cardboard, and also having compression elements arranged above the heating plates for acting on the sheet of corrugated cardboard.
Such a device in a corrugated cardboard facility has the function of drying glue between superimposed sheets, for example, one-sided sheets of corrugated cardboard and finally the cover sheet.
To this end, known devices have heating plates that are heated, for example, with steam or thermal oil. By means of a continuous transport belt, the sheet is conveyed through the heating zone. Compression elements press the sheets of corrugated cardboard against the surface of the heating plates in order to achieve an appropriate contact of the sheets of corrugated cardboard with the surface of the heating plates, that is, a good transfer of heat to the glue line.
In the case of one known compression unit shown in U.S. Pat. No. 5,632,830, weighted rollers are also used, which are affixed by intervening levers to a bearing arranged transversely to the advancing direction of the sheet of corrugated cardboard.
Further state of the art is also a compressing unit in the form of a pressure plate consisting of several units extending along the sheet of corrugated cardboard as shown in Canadian Patent No. 2,197,921. Also known is the use of pressure hoods shown in European Patent Publication EP 0,412,255 A1, as well as rollers shown in U.S. Pat. No. 5,632,830, which exert pressure on a circulating conveyor belt.
In order to avoid the disadvantages of the transport belt, it is also state of the art, as shown in U.S. Pat. No. 5,632,830, that the transport belt is eliminated and the sheet of corrugated cardboard is pressed directly against the heating surfaces by compression elements.
When the transport belt is dispensed with, however, automatic intake of the introduced sheets is no longer possible. Furthermore, eliminating the transport belt results in increased friction with the cardboard, and this increased friction produces frequent tears in the cardboard as it passes through the heating zone. Tears in conjunction with troublesome reinsertion bring about unacceptable production losses.